1. Field of Applicable Technology
The present invention relates to an apparatus for controlling the running condition of a motor vehicle, based upon respective values of rotational acceleration of the vehicle wheels, and in particular to a computation apparatus for computing the wheel acceleration, for use in such a running control apparatus.
2. Prior Art Technology
Various proposals have been made in the prior art for controlling running conditions of a motor vehicle on the basis of respective values of acceleration of the road wheels of the vehicle. It should be noted that in the following, "road wheel" will be simply referred to as "wheel", "wheel rotational velocity" is referred to simply as "wheel velocity", and "wheel rotational acceleration" is referred to simply as "wheel acceleration". Among such proposals are a constant-speed drive control apparatus whereby the vehicle speed is controlled to be held at a target speed, a traction control apparatus which controls the degree of wheel skidding during acceleration, and an anti-skid control apparatus for preventing locking of the vehicle wheels during braking. With such prior art types of vehicle running control apparatus, the wheel acceleration is used to directly express any change in the running condition of the wheels. Since information which expresses a value of acceleration will also indicate whether this is actually acceleration or deceleration, excellent control results can be obtained by implementing control on the basis of vehicle wheel acceleration in this way.
Generally with such an apparatus, successive values of instantaneous wheel velocity (i.e. each measured over a very short time interval) are successively obtained and temporarily stored, and successive values of instantaneous wheel acceleration are obtained from these values of instantaneous wheel velocity. In the case of the anti-skid control apparatus which is disclosed in Japanese Patent Laid-open No. 60-35649, designating the most recently obtained value of wheel velocity as V.sub.x0, the immediately previously obtained value of wheel velocity as V.sub.x1, the time interval over which V.sub.x0 was measured as .DELTA.T.sub.n, the time interval used for measurement of V.sub.x1 as .DELTA.T.sub.(n-1), then the instantaneous wheel acceleration V'W is given by the following equation: ##EQU1##
However the measured wheel velocity will include a large amount of high frequency noise components, resulting from vibration caused by the road surface, i.e. vibration of the vehicle and/or the attachment members which support the sensors used to measure wheel velocity). Since the instantaneous wheel acceleration is computed based upon this measured wheel velocity, the computed acceleration will also include large amounts of high frequency noise components. As a result, if control of the vehicle is directly executed based upon such a computed value of instantaneous wheel acceleration, then control failure can occur as a result of control processing becoming impossible to execute, due to the presence of such high frequency noise components.